1. Field of the Invention (Technical Field)
The present invention is in the field of a nanostructures and microstructures, use thereof in a memristor, and electronic memory elements.
2. Description of Related Art
A memristor (a portmanteau of “memory resistor”) was originally envisioned as a missing non-linear passive two-terminal electrical component relating electric charge and magnetic flux linkage. The above prior art memristor definition can be generalized to cover all forms of 2-terminal non-volatile memory devices based on resistance switching effects. The memristor is currently under further development.
When current flows in one direction through a memristor, the electrical resistance increases; and when current flows in the opposite direction, the resistance decreases. When a current is stopped, the memristor retains the last resistance that it had, and when the flow of charge starts again, the resistance of the circuit will be what it was when it was last active. It is believed that a prior art memristor device has a regime of operation with an approximately linear charge-resistance relationship as long as the time-integral of the current stays within certain bounds. Such provides a large area of uses.
Recently a development of a switching memristor based on a thin film of titanium dioxide took place, which relates to an on-off device. Such a device can be applied in nanoelectronic memories, computer logic, and neuromorphic computer architectures. Memristor technology can replace Flash, SSD, DRAM and SRAM memories. Typically a memristor is provided in an array, preferably built on a CMOS chip or the like, such as for applications in (neuromorphic) computer architectures.
A memristor can be characterized by experimental tests to determine if a device may properly be categorized as a memristor. In an example a memristor allows for a change in resistance that after a change therein remains constant, such that it can be used as a memory device.
It is noted that in principle many or all resistive switching memories are considered in this respect.
In a memristor an element is used having a relatively large electrical resistance, or likewise being not or at the most partly conducting. For that purpose insulators and possible semi-conductors are considered, such as the above titanium oxide. For contacting electrodes having conducting properties, such as metals, are used typically.
As a consequence existing memristors have various drawbacks. For instance functionality has yet to be demonstrated in operation at state of the art practical speeds, frequencies and densities. Further reproducibility may be an issue, as well as durability.
Electromigration is a process in which a metallic contact line is thinned by passing a current through it, thus gradually displacing atoms and ultimately leading to its destruction. In an atomistic approach, the electromigration process is the displacement of atoms from their crystal lattice position, hence requiring atoms to overcome the crystal lattice energy barrier. In this context it is important to point out that phonon scattering increases with increasing current, which in turn leads to an increase in the sample temperature (Joule heating). Thus part of the energy barrier is overcome by the temperature increase. An electromigration force is assumed to be a sum of two terms: an electrostatic force and a wind force. The electrostatic force is the direct force on an atom or ion in a material within an electric field. The wind force corresponds to the momentum transfer from the current carriers (electrons (electron-wind force) or holes (hole-wind force)) to atoms in scattering processes, such as grain-boundary scattering, surface scattering or phonon scattering.
In a continuum approximation, the damage created by electromigration can be described in terms of a combination of thermal and mechanical stresses, whereby the collapse will occur at the location of maximal thermomechanical stress. The thermal stress herein is due to the Joule heating of the sample during current passage. The mechanical stress herein arises from a change in the mass distribution due to electromigration-induced mass transport. Typically electromigration leads over time to destruction of an element, such as a contact line. Also electromigration typically is not reversible; an element is thinned at one end thereof.
Electromigration in pure metals such as copper has been investigated, but primary to study degradation of the metals.
The present invention relates to a nanobridge or microbridge and various aspects thereof which can be used in electromigration applications which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.